1. Field of the Invention
The present invention relates to a WDM device and a client device, and particularly relates to a WDM device, a client device, a system and a method for allocating wavelengths to a client signal.
2. Description of the Related Art
There are various techniques for transmitting client signals, such as SONET (Synchronous Optical Network), SDH (Synchronous Digital Hierarchy) and GbE (Giga-bit Ethernet) signals, via a WDM (Wavelength Division Multiplexing) network. Client signals can be mapped onto wavelengths for the WDM network in accordance with one of the schemes described below. It is to be noted that a connection rate (line band) of client signals is provisioned when installing additional client signal lines and the wavelengths are reserved corresponding to the line band of the client signals.
In a first mapping scheme, a single client signal is allocated a single wavelength. As shown in FIG. 1, an input client signal is supplied to a signal converting part 10. In the signal converting part 10, the input signal remains in its original format or is converted into a Digital Wrapper format or a format conforming to a wrapping technique defined by ITU-T G.709. The converted signal is transmitted on a wavelength that is unique within a WDM line 13. A multiplexer/demultiplexer (MUX/DEMUX) 12 multiplexes the plurality of wavelengths corresponding to a plurality of client signals to produce a wavelength-division multiplexed signal and transmits the wavelength-division multiplexed signal on the WDM line 13.
A multiplexer/demultiplexer (MUX/DEMUX) 14 demultiplexes the wavelength-division multiplexed signal from the WDM line 13 into a plurality of wavelengths, each of which corresponding to a single client signal. An inverse conversion is carried out in a signal converting part 16. The inverse conversion is an inverse of the conversion carried out at the signal converting part 10 of the sending side (i.e., to the original format, or, if Digital Wrapper format is used, the Digital Wrapper format is unformatted). The inverse converted signal is transmitted in the format of the original client signal.
In a second mapping scheme, a plurality of client signals is allocated a single wavelength. The second mapping scheme applies when the band of a client signal is sufficiently narrower than the band of a wavelength in the WDM network. As shown in FIG. 2, input client signals are supplied to a signal converting part 20 where the input client signals are time-division multiplexed or converted into a Digital Wrapper format or a format conforming to a wrapping technique defined by ITU-T G.709. The converted signal is allocated to a wavelength that is unique within the WDM line. A multiplexer 22 multiplexes the plurality of wavelengths corresponding to the converted signal to produce a wavelength-division multiplexed signal and transmits the wavelength-division multiplexed signal on the WDM line 23.
A multiplexer/demultiplexer (MUX/DEMUX) 24 demultiplexes the multiplexed signal from the WDM line 23 into a plurality of wavelengths. An inverse conversion is carried out in the signal converting part 26. The inverse conversion is an inverse of the conversion performed at the signal converting part 20 of the sending side (i.e., the time-division multiplexed signal is time-division demultiplexed, or, if Digital Wrapper format is used, the Digital Wrapper format is unformatted). The inverse converted signals are transmitted in a format of the original client signals.
In a third mapping scheme, a single client signal is allocated a plurality of wavelengths. The third mapping scheme applies when the band of a client signal is sufficiently broader than the band of a wavelength of the WDM network. As shown in FIG. 3, an input client signal is supplied to a signal converting part 30. In the signal converting part 30, the input client signal remains in its original format or is converted into a Digital Wrapper format or a format conforming to a wrapping technique defined by ITU-T G.709. In the signal converting part 30, the converted input client signal is further divided. The divided and converted signals are allocated a plurality of wavelengths that are unique within the WDM line. A multiplexer/demultiplexer (MUX/DEMUX) 32 multiplexes the plurality of wavelengths to produce a wavelength-division multiplexed signal and transmits the wavelength-division multiplexed signal on the WDM line 33.
A multiplexer/demultiplexer (MUX/DEMUX) 34 demultiplexes the wavelength-division multiplexed signal from the WDM line 33 into a plurality of wavelengths. An inverse conversion is carried out in the signal converting part 36. The inverse conversion is an inverse of the conversion performed at the signal converting part 30 of the sending side (i.e., the original format is left as it is, or, if Digital Wrapper format is used, the Digital Wrapper format is unformatted). The inverse conversion is carried out while synchronizing signals of each wavelength. The inverse converted signal is transmitted with a format of the original client signal.
FIG. 4 is a block diagram showing an example of a signal converting part of the related art. The signal converting part shown in FIG. 4 corresponds to the signal converting parts 10 and 16. In FIG. 4, a SONET/SDH client signal is received at a signal receiving part 40. A wrapping process part 41 converts the received signal into a Digital Wrapper format or a format conforming to a wrapping technique defined by ITU-T G.709. Then, in a wavelength allocating part 42, the converted signal is allocated a wavelength that is unique within a WDM line and then supplied to the multiplexer/demultiplexer 12 on the WDM line side.
On the other hand, a signal receiving part 45 receives signals that have been demultiplexed in the multiplexer/demultiplexer 14 of the WDM line side. The received signals undergo an unwrapping process (a conversion that is an inverse of the transform performed at the wrapping process part 41) in an unwrapping process part 46. Then, the signals are output from a SONET/SDH signal process part 47 as client signals of a SONET/SDH type.
Recent technical innovation provides an ever increasing capacity of a client signal (e.g. 40 Gbps) and an ever increasing capacity of a WDM line (increased number of wavelengths and increased capacity per wavelengths). However, since the rate of increase of the capacity of a wavelength of the WEM line is less than the rate of increase of the capacity of the client signal, a plurality of wavelengths will be allocated to a single client signal having a large capacity. As a result, the number of client signals that can be accommodated in the WDM line becomes less.
For example, when a client signal (OC768) of a SONET type with a line capacity of 40 Gbps is connected to the signal converting part 30 shown in FIG. 1, four 10.7 Gbps-wavelengths are allocated for transmitting all of the 40 Gbps capacity. However, when only two 10 Gbps SONET paths (OC192c) are actually used in the client signal line of 40 Gbps, only two of the allocated 10.7 Gbps-wavelengths are used and the remaining two wavelengths will be unused. The unused allocated wavelengths cannot be used for other lines. Therefore, there is a problem that wavelengths in the WDM line are not used in an efficient manner.